Synthesis of Various Branched Ultra-High-Molecular-Weight Polyethylenes Using Sterically Hindered Acenaphthene-Based α-Diimine Ni(II) Catalysts

Abstract

A series of highly sterically hindered acenaphthene-based α-diimine nickel complexes with the remote R group in 4-position of diarylmethyl moiety have been synthesized and characterized. Activated with Et 2 AlCl, ethylene polymerization by these nickel complexes is investigated in detail, involving the remote substituent effect and influence of polymerization temperature on catalyst activity, thermal stability, polymer molecular weight, and branching density. These thermostable nickel catalysts are very active (up to 5.1 × 10 6 g•mol −1 •h −1 ) for ethylene polymerization and capable of producing various moderate to highly branched (26−71/1000 C) ultra-high-molecular-weight polyethylenes (UHMWPEs, M w up to 4.5 × 10 6 g•mol −1 ). These polymeric materials with such unique structure show properties characteristic of thermoplastic elastomers, i.e., good elastomeric recovery and high strain at break.

Unsymmetrical Strategy Makes Significant Differences in α‐Diimine Nickel and Palladium Catalyzed Ethylene (Co)Polymerizations

“…Numerous studies have disclosed a rule that increasing steric bulk results in the increase of polymer molecular weight in α-diimine Ni(II)-catalyzed ethylene polymerization [20,22,28,29,44] . However, we found in 5 min that unsymmetrical Ipty/Ph-Ni produced significantly higher polymer molecular weights (741 kDa to 1230 kDa) than those generated by symmetrical Ipty-Ni and Ph-Ni (90 kDa to 356 kDa).…”

“…As a comparison, tuning on ligand sterics is considered to be much more important. Guan, [25,26] Rieger, [27] Long, [28][29][30] Coates, [31][32][33][34] Brookhart and Daugulis, [35][36][37] Sun, [38 Gao, [39,40] Chen [41][42][43] and Dai [44][45][46] successively developed versatile sterically encumbering N-aryl substituents such as cyclophane, dibenzhydryl, and "sandwich"-type moieties and bulky backbone such as dibenzobarrelene. Moreover, Chen, [42,43,47,48] Sun [49][50][51][52][53][54][55][56][57][58][59] and Milani [60][61][62][63] independently developed a series of unsymmetrical α-diimine catalysts which contained different steric bulk and systematically studied their polymerization properties.…”

A continuing legend: the Brookhart-type α-diimine nickel and palladium catalysts

“…3) possessing different X substituents (OMe, Me, t Bu and Ph) were also synthesized. 64 All of these catalysts were highly catalytically active at the level of 10 6 g PE (mol Ni h) −1 toward ethylene polymerization, and yielded semicrystalline polyethylenes with M n values larger than one million. In addition, these catalytic systems maintained high catalytic activity and high M n values at temperatures of up to 100°C.…”

“…,6-Diarylhydryl-based α-diimine Ni and Pd catalysts. 57-,6-Dibenzhydryl-based α-diimine Ni catalysts 63,64. …”

Monodentate aminophosphine nickel(II)‐ and palladium(II)‐catalyzed ethylene oligomerization and norbornene polymerization

“…Olefin polymerization and oligomerization have been playing critical roles in the chemical industry, since polyolefins represent almost half of the world's plastics annual production, and oligomers of olefins represent an important route to the production of synthetic lubricants, gasoline additives and kerosene fuels . In the past few decades, late‐transition‐metal catalysts have received much attention in the field of olefin polymerization and oligomerization, especially Brookhart's α‐diimine Ni(II) and Pd(II) catalysts (Scheme A), Grubbs's phenoxyminato Ni(II) catalysts (Scheme B), Keim's SHOP‐type Ni(II) catalysts (Scheme C) and Drent's phosphinesulfonate Ni(II) and Pd(II) catalysts (Scheme D) . More generally, various bidentate chelating ligands with N^N, N^O, P^O, P^P (Scheme E) and P^N (Scheme 1F) donor atoms have been explored for late‐transition‐metal‐catalyzed olefin polymerization and oligomerization .…”